The "Use modern interface for signing and Digital ID configuration" was freezing the application whenever my users are trying to sign a document. The workaround was to go to Preferences > Signatures > Creation & Appearance to uncheck "Use modern interface for signing and Digital ID configuration".
I came across this forum which was A BLESSING. Go to the bEnableCEFBasedUI section for the original content.
https://www.adobe.com/devnet-docs/acrobatetk/tools/PrefRef/Windows/Security.html#idkeyname_1_24812
If you want the fix to apply to all profile on a machine, go to your registry editor. Path: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\Adobe Acrobat\DC\FeatureLockDown\cSecurity\cPubSec. Create two DWORD values bEnableCEFBasedUI and bSelfSignCertGen. Set them to 0.
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